The present invention relates to a method and apparatus for measuring the crimp frequency in crimped tow or yarn, and more particularly to such a method and apparatus which is suitable for use in an automatic on-line, or in situ, operation.
In modern fiber technology, a number of continuous man-made fiber filaments are gathered together in loose, rope-like form to make a large strand of material, commonly referred to as "tow". The tow is cut into suitable lengths as staple and processed on a spinning system. The loose filaments in the tow are usually held together by means of crimp which is placed in the tow during a fiber texturing process. In addition to holding the filaments of the tow together, the crimp also serves to add bulk to the material.
The crimp frequency of tow is a definition of the waviness of the fiber and is expressed in terms of crimps per unit length, e.g. crimps per inch. The measurement of crimp frequency can be used as a quality control step in determining the texture of the fiber being processed.
In the past, the measurement of crimp frequency has been carried out off-line in a laboratory by an operator using a scaled ruler and a tensioning device. A predetermined tension is placed on a representative sample of the tow to remove low frequency secondary crimp therefrom, and the ruler is layed on top of the tow. The operator visually counts the number of crimps in a unit length of the tow, such as one inch, for example, to determine the crimp frequency of the tow.
Since this prior art method for measuring crimp frequency is an off-line operation, the difference between the time when the crimp frequency of tow being produced goes outside of predetermined control limits and the time when this deviation can be detected is substantial and often unsatisfactory, and may result in wasted material. In addition, the visual inspection of each measured tow sample by an operator is subject to frequent error and is a very tedious operation which seriously limits the amount of testing that can be performed by a single operator.
One proposed method for automatically evaluating the properties of crimp in a crimped tow or yarn is disclosed in U.S. Pat. No. 3,333,467. In the operation of the apparatus disclosed in this patent, a tension sufficient to substantially straighten the bends in the tow is placed on the tow by tensioning rollers. The tow is then passed between two relaxing rollers which reduce the tension on the tow, allowing the crimp in the tow to recover and maintain a tension on the tow. The magnitude of this tension is sensed by a tension-sensing roller, to provide an indication of the crimp angle, crimps per inch and modulus of elasticity of the fiber comprising the tow. The method and apparatus proposed by this patent are not entirely satisfactory, since they are not capable of measuring crimp frequency per se. Rather, crimp frequency can only be detected in conjunction with the other above-mentioned factors affecting the tension of the tow. In addition, the speed ratio of the relaxing rollers to the tensioning rollers has an effect upon the measurement; and therefore may not provide uniform results during different testing operations.
Another proposed method for measuring crimp frequency is disclosed in U.S. Pat. No. 4,057,350. In the operation of the apparatus disclosed in this patent, a crimped fiber is placed within a specimen cell and a laser beam is passed through the cell while the cell is moved in a direction transverse to the beam and lengthwise of the fiber. Each crimp in the fiber deflects the laser beam and the deflections are received as pulses of light by a photodetector. The photodetector actuates a counter to provide a count indicative of the number of crimps in the fiber. Although the apparatus disclosed in this patent is capable of measuring crimp frequency per se, it is only capable of detecting the crimp frequency in a single strand of fiber. It is not adapted for use with a strand of tow comprising a large number of filaments, and is therefore not suitable for on-line use during the production of tow. In addition, the need for laser light renders the frequency measurement system of this patent economically unfeasible.
It is therefore a general object of the present invention to provide a novel method and apparatus for measuring the crimp frequency of crimped tow.
It is another object of the present invention to provide a novel method and apparatus for automatically measuring crimp frequency to thereby eliminate the need for manual measurements of crimp frequency.
It is a further object of the present invention to provide a novel method and apparatus which is adapted for on-line measurement of crimp frequency during the production of crimped tow.
It is yet another object of the present invention to provide novel apparatus for clamping and tensioning tow to remove secondary crimp therefrom during the measurement of the primary crimp frequency of the tow .